diff --git a/firmware/controllers/math/efitime.h b/firmware/controllers/math/efitime.h
index 386bb84607..11aabafe94 100644
--- a/firmware/controllers/math/efitime.h
+++ b/firmware/controllers/math/efitime.h
@@ -39,6 +39,9 @@ extern "C"
  *
  * By using 64 bit, we can achieve a very precise timestamp which does not overflow.
  * The primary implementation counts the number of CPU cycles from MCU reset.
+ *
+ * WARNING: you should use getTimeNowNt where possible for performance reasons.
+ * The heaviest part is '__aeabi_ildivmod' - non-native 64 bit division
  */
 uint64_t getTimeNowUs(void);
 
diff --git a/firmware/controllers/trigger/main_trigger_callback.cpp b/firmware/controllers/trigger/main_trigger_callback.cpp
index 1e06f52b95..d526173097 100644
--- a/firmware/controllers/trigger/main_trigger_callback.cpp
+++ b/firmware/controllers/trigger/main_trigger_callback.cpp
@@ -225,6 +225,7 @@ void showMainHistogram(void) {
 #endif
 }
 
+// todo: eliminate this 'extern'
 extern Engine engine;
 
 /**
diff --git a/firmware/controllers/trigger/rpm_calculator.cpp b/firmware/controllers/trigger/rpm_calculator.cpp
index 7dd19ed130..9c446db39b 100644
--- a/firmware/controllers/trigger/rpm_calculator.cpp
+++ b/firmware/controllers/trigger/rpm_calculator.cpp
@@ -102,17 +102,17 @@ bool isCranking(void) {
  * This callback is invoked on interrupt thread.
  */
 void rpmShaftPositionCallback(trigger_event_e ckpSignalType, uint32_t index, RpmCalculator *rpmState) {
+	uint64_t nowUs = getTimeNowUs();
 
 	if (index != 0) {
 #if EFI_ANALOG_CHART || defined(__DOXYGEN__)
 		if (engineConfiguration->analogChartMode == AC_TRIGGER)
-			acAddData(getCrankshaftAngle(getTimeNowUs()), 1000 * ckpSignalType + index);
+			acAddData(getCrankshaftAngle(nowUs), 1000 * ckpSignalType + index);
 #endif
 		return;
 	}
 	rpmState->revolutionCounter++;
 
-	uint64_t nowUs = getTimeNowUs();
 
 	bool hadRpmRecently = rpmState->isRunning();
 
diff --git a/firmware/hw_layer/microsecond_timer.c b/firmware/hw_layer/microsecond_timer.c
index 460277d47b..c51e3bdc65 100644
--- a/firmware/hw_layer/microsecond_timer.c
+++ b/firmware/hw_layer/microsecond_timer.c
@@ -22,7 +22,7 @@
 
 #define GPTDEVICE GPTD5
 
-static volatile uint64_t lastSetTimerTime;
+static volatile uint64_t lastSetTimerTimeNt;
 static int lastSetTimerValue;
 static volatile bool isTimerPending = FALSE;
 
@@ -45,7 +45,7 @@ void setHardwareUsTimer(int32_t timeUs) {
 		gptStopTimerI(&GPTDEVICE);
 	gptStartOneShotI(&GPTDEVICE, timeUs);
 
-	lastSetTimerTime = getTimeNowUs();
+	lastSetTimerTimeNt = getTimeNowNt();
 	lastSetTimerValue = timeUs;
 	isTimerPending = TRUE;
 	timerRestartCounter++;
@@ -85,7 +85,7 @@ static msg_t mwThread(int param) {
 	while (TRUE) {
 		chThdSleepMilliseconds(1000); // once a second is enough
 
-		if (getTimeNowUs() >= lastSetTimerTime + 2 * US_PER_SECOND) {
+		if (getTimeNowNt() >= lastSetTimerTimeNt + 2 * CORE_CLOCK) {
 			strcpy(buff, "no_event");
 			itoa10(&buff[8], lastSetTimerValue);
 			firmwareError(buff);
@@ -94,7 +94,7 @@ static msg_t mwThread(int param) {
 
 		msg = isTimerPending ? "No_cb too long" : "Timer not awhile";
 		// 2 seconds of inactivity would not look right
-		efiAssert(getTimeNowUs() < lastSetTimerTime + 2 * US_PER_SECOND, msg, -1);
+		efiAssert(getTimeNowNt() < lastSetTimerTimeNt + 2 * CORE_CLOCK, msg, -1);
 	}
 #if defined __GNUC__
 	return -1;
@@ -111,7 +111,7 @@ void initMicrosecondTimer(void) {
 
 	gptStart(&GPTDEVICE, &gpt5cfg);
 
-	lastSetTimerTime = getTimeNowUs();
+	lastSetTimerTimeNt = getTimeNowNt();
 #if EFI_EMULATE_POSITION_SENSORS
 	chThdCreateStatic(mwThreadStack, sizeof(mwThreadStack), NORMALPRIO, (tfunc_t) mwThread, NULL);
 #endif /* EFI_ENGINE_EMULATOR */
diff --git a/unit_tests/test_trigger_decoder.cpp b/unit_tests/test_trigger_decoder.cpp
index c120f61b76..f7c11eaf57 100644
--- a/unit_tests/test_trigger_decoder.cpp
+++ b/unit_tests/test_trigger_decoder.cpp
@@ -339,11 +339,16 @@ void testGY6_139QMB(void) {
 
 extern EventQueue schedulingQueue;
 
+// this is a very dirty and sad hack. todo: eliminate
+extern Engine engine;
+
 static void testRpmCalculator(void) {
 	printf("*************************************************** testRpmCalculator\r\n");
 
 	EngineTestHelper eth(FORD_INLINE_6_1995);
 
+	efiAssertVoid(eth.engine.engineConfiguration!=NULL, "null config in engine");
+
 	initThermistors(&eth.engine);
 
 	engine_configuration_s *ec = &eth.persistentConfig.engineConfiguration;
@@ -354,6 +359,9 @@ static void testRpmCalculator(void) {
 	ec->globalFuelCorrection = 3;
 	eth.initTriggerShapeAndRpmCalculator();
 
+	// this is a very dirty and sad hack.  todo: eliminate
+	engine.engineConfiguration = eth.engine.engineConfiguration;
+
 	configuration_s configuration = { ec, ec2 };
 	timeNow = 0;
 	assertEquals(0, eth.rpmState.rpm());